1. Field of the Invention
The present invention relates to color display systems. More specifically, the present invention relates to the use of a two-channel field sequential color display system for generating high resolution, full color images from an electronic source.
2. Description of the Related Art
There is a need for low cost, high resolution color display systems for use in large screen, high-definition television sets and other commercial, industrial, training and entertainment display products. Current technology cannot deliver, at an affordable cost, either the resolution or the high light output required for viewing in an acceptable ambient lighting environment.
Prior color display systems that generate full color images from an electronic source fall into three categories: (1) Additive color Systems, (2) Single-Channel Field Sequential Color Systems and (3) "Spatial Multiplexing" Systems. In additive color display systems, such as those described by H. Noda et al. "High Definition Liquid Crystal Projection Television", Japan Display '89--Proceedings of the Ninth International Display Research Conference, Oct. 16-18 1989, 256-259 (1989), the three primary colors (red, green and blue) are displayed using three separate image sources (channels). The three channels project three different color representations of the same image simultaneously such that the three separate images overlap at an image plane. The three color images "add" up to give an accurate full color representation of the image. The main problem with this approach is cost. Three separate image sources are required, each with its own set of associated optics. Another problem is size. The higher the number of channels, the larger the system. In addition, a complicated projection lens is usually required with this approach.
In single-channel field sequential color systems, such as the Tektronix model Nu900M color monitor, a single image source or channel is used. The three primary color images are displayed sequentially during one display frame. Display frame rates are typically 60 Hz (1/60 of a second per frame). The three primary color images are displayed in sequence at a rate that is four times the frame rate (typically 180 Hz) so that all three color images are displayed over the course of one frame. This technique is preferable over additive systems in terms of cost and complexity because only one image source is used.
The main disadvantage of field sequential color systems is reduced light output (luminance). This is due to the fact that only one image source is used. Each separate color image is displayed for only one-third of a frame as compared to a full frame in the additive system. In addition, since the intensity distribution of the image will change according to which color is being displayed, the image source must be able to respond or switch in 1/180 of a second as opposed to 1/60 of a second in an additive system (all three color image sources remain static for one full frame in an additive system). A third problem with this approach has to do with the response of the human eye. For typical conditions of display luminance, surround luminance and ambient lighting, most observers see the three sequential color images as if they were projected simultaneously. However, a segment of the viewing population observes a red and/or green and/or blue color flashes (temporal visual effects) as a result of the sequential displaying of the three color images.
The spatial multiplexing approach is the basis for most color television sets. In this approach, three color dots or stripes are placed in close proximity to each other and are used to represent one image pixel. This three dot or three stripe structure generates the sensation of color. However, the field of view is limited with this approach because the merging of the three color dots or stripes into a single combined color only works if the width of the three color dots or stripes subtends a smaller angle at the eye than the visual acuity of the eye. For example, a 1,000-line, 3,000-stripe device has a maximum obtainable field of view of only 33 degrees.